const net = require('net');

const wait = ms => new Promise(resolve => setTimeout(resolve, ms));

const probeTcpPort = (host, port, timeoutMs = 500) =>
    new Promise(resolve => {
        const socket = net.createConnection({ host, port }, () => {
            socket.end();
            resolve(true);
        });
        socket.on('error', () => resolve(false));
        socket.setTimeout(timeoutMs, () => {
            socket.destroy();
            resolve(false);
        });
    });

/** Something is accepting connections on this port. */
const isTcpPortBusy = (host, port) => probeTcpPort(host, port);

/** True if we can bind — more reliable than connect probe before GDB Server starts. */
const canBindTcpPort = (host, port) =>
    new Promise(resolve => {
        const server = net.createServer();
        server.once('error', () => resolve(false));
        server.listen({ host, port }, () => {
            server.close(() => resolve(true));
        });
    });

const waitUntilTcpPortFree = async (host, port, timeoutMs = 10000) => {
    const startedAt = Date.now();

    while (Date.now() - startedAt < timeoutMs) {
        if ((await canBindTcpPort(host, port)) && !(await isTcpPortBusy(host, port))) {
            return;
        }
        await wait(200);
    }

    throw new Error(
        `TCP 포트 ${port}(${host})이 아직 사용 중입니다. JLinkGDBServerCL을 종료한 뒤 몇 초 기다려 주세요.`
    );
};

const assertTcpPortFree = async (host, port, label = 'RTT') => {
    if (await canBindTcpPort(host, port)) return;

    throw new Error(
        `${label} 포트 ${port}(${host})이 이미 사용 중입니다. Receiver/Transmitter를 Stop한 뒤 몇 초 기다리거나, 작업 관리자에서 JLinkGDBServerCL 프로세스를 종료하세요.`
    );
};

module.exports = {
    isTcpPortBusy,
    canBindTcpPort,
    waitUntilTcpPortFree,
    assertTcpPortFree,
};